dual ported exhaust muffler

[darrenjttu]

I am about to buy a stihl 390 and was wondering if dual ported mufflers make a big difference.

[joe_indi]

The MS390 has a nice mid range power.A dual port would only enhance it more. But, I dont see an OEM dual port in the parts list.So you will need to get the original muffler and its cover modified

[Al_Smith]

Unless they've changed them as I recall the 029-039 uses a one piece muffler .To get any preformance gains you'd about have to uncrimp the muffler halves to remove the baffle cage.

[joe_indi]

Al,
I think you might be referring to the 021/23/25 muffler, which you have to uncrimp to widen the outlet.
The 029, 39  have a cover on their mufflers which comes off if you remove the 3 holding nuts.
Here is a picture:


Joe

[Al_Smith]

Sure that's exactly like the one in a box in my shed .The fact remains though just how would a person cut the baffles out if you can't get more than just a little hole in the front to work through?If you didn't cut the baffles loose a multi ported muffler wouldn't really help that much .

When I get a chance I'll more carefuly scrutinize that box of parts to see if there might be a simple solution .

[darrenjttu]

I found a guy who can modify one for 40 buck. Is it worth it?

[woodtech]

I was shown a pretty neat modification from a friend.  Under the cover of the muffler you'll see the indented part of the muffler face.  That's the end of the internal baffle.  Drill five holes there and two more above the baffle.  Then, the face plate needs to look more like the standard face plate in the above diagram.  So, grind away the angled part.  In a nutshell, the recipe for getting power back is drill and grind away at unnecessary epa restrictions. 

[AdkStihl]

When modifying an exhaust, its better to make one larger hole than it is to make many small holes. The single large hole will have less surface area (drag) on the hot exhaust gasses. Also...keep in mind that exhaust gasses will flow much quicker through a rounded or radiused(sp) opening.

[Al_Smith]

Couple evenings ago a guy from work stopped over for help with an 048 Stihl which we got going .He had brought with him an 029 that he had installed an aftermaket 039 cylinder on .

Evidently he had pulled the little cover on the muffler front and drilled a big hole through the baffles from what he said .Now I ran it and for basically an 039 it did fine .Then of course being a smart alec I pulled down an 038AV from the shed which was "enhanced " and showed him how a pro grade saw can run . ;)

None the less the revamped 029/039 did pretty good ,better than most I've seen .

[Cut4fun]

290 310 390 muffler mod and carb retune takes about 30mins of your time for about 20% gains.  Easy DIY project.

Dont get took by those online expensive muffler sellers.